Enzymatic conversion of soapstock fatty acids from oil refining waste to biosurfactant using a low-cost liquid lipase and a new application as an antioxidant

Polyglycerol fatty acid ester (PGFE) is one kind of non-ionic biosurfactant with excellent emulsifying property, physicochemical stability, and biodegradability. In this work, a low-cost liquid lipase Candida antarctica lipase B (CALB) was used as an eco-friendly biocatalyst to promote the esterification of polyglycerol-3 (PG3) and fatty acids (FA) from soybean oil waste soapstock for PGFE production. Effects of lipase load (0.1–0.6 wt%), reaction temperature (50–100 ℃), substrate ratio of PG3 to FA (1.0:1–2.0:1, mol/mol), and time (0.5–12 h) on the esterification were evaluated and optimized by central composite design. The high FA conversion (84.31%) was obtained under the optimal conditions: 0.54 wt% lipase load, 1.5:1 molar ratio of PG3 to FA, 84 °C, and 5.8 h. In PGFE products, the contents of mono-ester, di-ester, and tri-ester were 43.77%, 39.03%, and 17.20%, respectively. Additionally, PGFE showed excellent in vitro antioxidant efficiency and decreased 62% peroxide value in soybean oil system after 21 h of storage at 105 ℃. Graphical abstract